# How should I scale the Solar System for my video game?

I am making a multiplayer video game, and am wondering how I should scale the in-game universe. The game has pseudo-realistic travel, but I want the scaling to be large enough to offer challenging gameplay.

I have already determined the Sci-Fi portions of my game (in which an evil Monsanto-like corporation got nuked out of Mars and escaped using an Orion-like ship), and the technology in the game is fairly advanced. I would like a reasonable scale keeping this in mind, perhaps for travels up to a month or two for crazy explorers.

How should I scale the Solar System for my video game?

• What are you looking to scale it against? Humans traveling in spaceships? Roughly what technology level do they have? Fusion-powered? Edit your question and add some more details and we'll be able to help you more. – john3103 Oct 10 '13 at 1:15
• I see this being in 3 parts: 1. What is a realistic size for a solar system. 2. What is a realistic speed for in-solar system activities. 3. What is the size of the planets/star, given such. Each could easily be given their own question. – PearsonArtPhoto Oct 10 '13 at 1:57
• Right - it mostly boils down to "How long should it take to get from Mars to Jupiter" and what sort of sci-fi bits dragutux is going to need to make that happen. – john3103 Oct 10 '13 at 2:02
• Theorically players have engines reaching from the space farmer class to space carriers/space truckers gigawatts are the norms of measurement with several grades (likely to be a fusion matter solution involved) to answer : 1 : size on our current solar system as a "base" 2 : speed is calculated by factors but scale of the game will determine it, the longer you would travel, the harder it'll be to do so (point of non return & fuel calculations involved based + "tech level" + ship fitting 3 : the scale would be globally adapted from distances to planetoids objects :) – user871 Oct 10 '13 at 2:09
• I like this question, but I'm afraid it's going to need a little more work to be answerable. Are your players going to be limited to traveling within the solar system? Or can they perform instellar travel? What is your main constraint? The time that it takes or the speed that they travel? – called2voyage Oct 10 '13 at 12:48

Okay, let's just take a few hypothetical situations here and see what we can come up with. You specifically mentioned going from Mars to Jupiter, and want something realistic, but quick. Let's assume you have a 1g acceleration capability. How you do that is up to your game really. To make things a bit simpler, I'm going to have two modes of operation, which should bound pretty well how long it will take. I'm going to assume you want to stop there, and not just flyby. They are:

1. Mars/Jupiter at closest approach. Will add in a bit of time to match the different relative velocities, and ignore inclination, etc.
2. Mar/Jupiter at furthest apart. Will assume that one losses all Martian speed, heads straight to Jupiter, then gains all of the Jupiter speed.

These aren't quite accurate, but they are close enough. Okay, so here's a few key facts:

• Jupiter- Distance= 778,500,000 km, orbital velocity= 13.07 km/s
• Mars- Distance= 227,900,000 km, Orbital velocity= 24.125 km/s.

The time given a 0 starting speed, 0 ending speed, straight line, and half accel, half decel can be found by:

$\sqrt{2*\text{dist}/a}$

Okay, so, what do we have? Let's start with the maximum distance case. Distance is added, so 1,006,400,000 km. Plugging that in to the above formula, that gives us 453197 s, or about 125.9 hours. Adding in the relative speed difference will take another 3795 seconds, or a bit more than an hour. Thus, I'll say 127 hours should be sufficient.

How about the best case scenario? The distance is reduced to 550,600,000 km. Plugging it in to the same formula gives 335212 s, or 93 hours. The relative speed difference will be 1128 s, or only a fraction of an hour.

If you use a higher speed, the time will decrease by the same formula, just use a different value for a other than $9.8 m/s^2$. It seems likely that humans could accelerate at 3 g for some time, which would reduce the time by almost a factor of 2 to make this work. Beyond that, you need some sort of an inertial dampener.

• While this is interesting, i did not speak about jupiter or mars... and the calculations are already done (but have to be adjusted along some alpha testing). The question was : how scalable would it be at (for example a 1/5 scale : would that be reasonnable ? the idea is that i will setup solar systems that are viable but are in no way as big as the real ones... or maybe one will be for a battle, who knows, there will be variations :). Point is : travelling speed is not the matter there.. scaling is :). – user871 Oct 11 '13 at 3:41

In terms of interplanetary travel-time, there's a couple of different limits that are overcome as the presumptive technology-level increases (AKA sci-fi):

1.) Limited by Energy: spacecraft use a boost-and-coast method with gravity-assists where possible from planetary bodies along the way. (this is where human space-travel is at right now). Limited to speeds of 5-15 kilometers/second, depending on how large a craft and how much one can spend on fuel and what gravity-assists we can get. Travel from Earth to Jupiter (~4 AU) takes many months. Voyager 1 did it in 16 months. Humans traveling in space have HUGE limitations and it's terribly expensive and dangerous.

2.) Limited by Inertia: If we were able to get LOTS of energy into a spacecraft, i.e. fusion-power or antimatter, etc. and a way to generate lots of thrust with little reaction-mass (aka a plasma-drive), we'd be able to constantly accelerate a craft on a trip. With humans on-board, we'd generally be limited to 1-2 g's of acceleration (to avoid injuring or killing passengers). Travel between planets in our solar system would generally be a matter of days. Unmanned craft could go even faster, accelerating at 5-10 g's - depending on how well-build the craft is.

Depending on how good our power and thrust generation is, we could get to nearby stars in a matter of a few generations (i.e. ~100 years to get to Tau Ceti) - so interstellar colonies are a possibility.

3.) Limited by Lightspeed: If we then developed some way to reduce or eliminate inertia (i.e. manipulating the Higgs boson ) and could accelerate as much as we wanted so long as speeds were below lightspeed. Travel between planets would be a matter of 5-25 minutes between inner planets (Mars to Venus for example), and outer planets are a matter of hours (Jupiter to Neptune and the like)

Interstellar travel would still take 5-20 years to get between the near star systems (5-10 light-years) depending on exactly what percent of c we were able to achieve.

4.) Faster-Than-Light travel: Wormholes and Warp-Drive - the sky's the limit here. Travel could be instantaneous or still take elapsed time. It all depends on how you want your sci-fi universe to work.

• I'm bad at physics so please excuse me if this sounds naive, but what do you mean when you say "limited by inertia"? Do you mean that we would need to decelerate half the way through? – System Down Oct 10 '13 at 18:57
• @SystemDown He means that we could only accelerate so fast before it would cause damage. – called2voyage Oct 10 '13 at 19:17
• @SystemDown - called2voyage is correct. Although I should add that the "Constant Acceleration" method means one speeds-up for the first half of the voyage, then you flip the ship around and decelerate for the 2nd half. I.e. to match speeds with the destination. – john3103 Oct 10 '13 at 20:16
• @called2voyage Ah ok gotcha! – System Down Oct 10 '13 at 20:49
• I'm voting this as a productive answer, however, the problem is more of providing a viable large enough system for a game. again, traveling to a planet is likely to take 25 mins to a moon, traveling is hard. anyway the speed calculation "faking" it : i have numerous solutions, again : not the issue; in fact it will be almost impossible for players to travel using engines even with a powerfull one. Referal speed : backstory state that the original ship took 400K Years to go trough an interstellar gap. – user871 Oct 11 '13 at 3:56